96 F150 I6 still running badly

Hi folks

Thanks again for all the help on my previous thread. My truck still runs like crud, though I now see a pattern which may help.

Truck is a 96 F150 with a straight 6, fuel injected. Symptom is it starts fine when cold, and actually runs OK until it gets to operating temp. Once at temp, the engine stumbles badly when I give it more than

1/2 pedal on the accelerator. More run time, and almost any gas makes it run like it's on 5 cylinders. Restarting when hot is almost impossible, but a cold restart is fine.

Here's what I've done so far: Replaced - plugs, air filter, oil, fuel filter, cap, rotor. Removed and sprayed down 5 injectors, replaced one because my father in law broke it (long story) Checked vacuum at the brake booster port on the upper intake manifold. Reading very steady 20 at idle, accel drops to about 5 and quickly rebounds back to 20. When I hold a higher RPM it drops very little. I don't have a tach, but I estimate the RPM to be around my shift point. Tried various points, higher the RPM, less vacuum. But the lowest it gets to is about 18-19.

Vacuum readings seem to rule out clogged exhaust, though I may be mistaken.

I also pulled the throttle body and cleaned the heck out of it. Used

1/2 bottle of SeaFoam cleaned through PCV hose, let sit about 10 minutes and ran it out at idle. Repeated again, this time letting sit for several hours.

Codes - I only have the original list of codes. They list All O2 sensors reading a lean condition Crankshaft Position Sensor not working. (I missed this one before) Misfire cylinder 1

Can the crank position sensor be causing this? I don't even know what this would do in this vehicle, as I have a conventional distributor with rotor.

I'm at a loss as to what to change next, though maybe I should be replacing the other five injectors. The hot vs. cold conditions aren't making sense to me though...

Thanks,

-ben

Reply to
Ben Snyder
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Does it "chug" black smoke when it's running rough?

Spdloader

Reply to
Spdloader

From what I can see, no. But it's hard to tell because I wasn't looking for it... I will take it for a run later until it runs badly, then will look again.

What would the black smoke indicate? I know it would be running rich, but in terms of a cause?

-ben

Reply to
Ben Snyder

Quick addition - alldatadiy.com indicates that my truck has a Crankshaft Fluctuation Sensor - it reads pulses from the rotating crankshaft and registers misfires. Maybe this is what the OBDII code is trying to day is faulty?

OBDII code is P0385

-ben

Ben Snyder wrote:

Reply to
Ben Snyder

IF it is chugging or smoking, the manifold air temperature sensor/intake air temperature sensor (I forget which one it's called on a Ford) can go bad and tell the computer it's -20 below outside. This richens the mix, and will cause all the symptoms you are describing, but usually there is some black (unburned fuel) smoke as well as black or foul-looking plugs.

Spdloader

Reply to
Spdloader

Ah, ok. The plugs looked fine when I replaced them.

-ben

Reply to
Ben Snyder

Adversely, the sensor can go the other way, and make the system run lean. Not impossible, but unusual.

Spdloader

Reply to
Spdloader

UPDATE - Replaced all fuel injectors with new. Runs maybe 70-80% better now. Vac was testing fine until I replaced these, now I'm dropping as low as 14-15 at RPMs higher than idle.

Front cat looks clogged, maybe up to 50% clogged. Not good. Rear

*looks* fine. I plan on testing with them out later today, if this is the problem then one or two new cats will be on the way.

-ben

Ben Snyder wrote:

Reply to
Ben Snyder

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